I am looking for papers, books or any other resources which I can use to work in General Relativity with Maple. I know, there is GRTensor tool, but it is not up-to-date as far as I understand from its website (latest test was on Maple 11). I use Maple 15. Can you advise me something?
Explore build-in tensor package in Maple. As far as I know, it allows deal with tensors, their operations, and their use in General Relativity both in the natural basis and in a moving frame. Also visit Differential Geometry Library. There are hundreds of exact solutions of Einstein's equations with copyable formulas for Maple, Mathematica, MathML and LaTeX. Finally, atlas for Maple - doing calculations in modern differential geometry and its applications. There are some examples which may be interested for you: Kerr black hole Schwarzschild black hole with cosmological constant